The present invention relates to a process for mixing wet molding materials, particularly wet molding sands, used for casting purposes the process includes premixing the dry components of the molding materials in a container followed by adding the moist components of the molding materials and then homogenizing the dry and moist components by further mixing.
Known mixing processes for foundry molding materials of the aforementioned type are performed in a variety of different mixer constructions. However, it is common to all these mixers for there to be a stationary or rotary, trough-like container, which is provided on its circumference or bottom with a discharge opening and into which mixing tools of different types may be engaged. The dry components are filled into the container from the top and the addition of moist components takes place above the surface level of the dry components. The dry components are formed from granular, free-flowing bulk materials, such as new sand and worked up used sand, as well as finely divided, almost dry bulk materials, such as coal dust and the like. The moist components are binders or bonding agents and are mainly in the form of sodium-bentonite, comprising layer or laminated particles, which are activated and swell when water is added. The swelling can be attributed to the incorporation of water molecules into the laminated mineral. Water-glass is also sometimes used as the binder which dries with the addition of air to produce the bond. The moist binder or binder components, are fed in above the surface level of the dry components.
In the known mixing processes, the wet molding material is produced batchwise, with particular importance being attached to short mixing times, so that the molding machine can constantly be supplied with wet molding material. The complete mixing cycle, which is essentially determined by the nature of the mixing tools and the circulation rate within the mixer, is at least two minutes in the known processes.